Initiating device for an electronic detonator

ABSTRACT

This invention provides an initiating device  10  for an electronic detonator, which includes two spaced electrical conductors  12  located on an insulating substrate  14;  and two separate resistive means in the form of thick film resistive bridges  16  extending between the electrical conductors  12,  for releasing energy upon application of an electrical current to the resistive bridges  16.  An explosives or pyrotechnic composition, generally designated by reference numeral  18,  covers the resistive bridges  16.  It will be appreciated that should one of the bridges  16  fail, the other bridge  16  would still initiate the device  10.  The size of the contact interface between the bridge  16  and the explosives composition  18  is also doubled, making the initiating device  10  even more reliable. As a result the initiating device  10  is suitable for a wide range of different applications.

INTRODUCTION AND BACKGROUND TO THE INVENTION

[0001] This invention relates to an initiating device. More particularly but not exclusively this invention relates to a novel initiating device suitable for use with electronic detonators.

[0002] All known resistive initiating devices include a single resistive element that is connected by some or other means to, or is in close contact with, electrically conductive areas and/or current feed mechanisms so as to provide the necessary connection to the energy source required to cause ignition on functioning.

[0003] For example, a known detonator initiating device comprises two spaced electrical conductors; and a resistive element extending between the electrical conductors, for releasing energy upon application of an electrical current to the element. The resistive element is embedded in an explosives or pyrotechnic composition, which, in use, is ignited by the resistive element.

[0004] Further for example, U.S. Pat. Nos. 2,960,933; 3,763,782; 4,858,529; 5,544,585; PCT applications numbers WO95/11421 and WO98/45663; and Canadian patent number 1,150,513 all disclose a detonator or initiator having two spaced conductors connected by a single resistive element for releasing energy upon the application of an electrical current.

[0005] It is a requirement for any initiation system, in general, to have a high degree of operating regularity and a very high degree of reliability. A disadvantage of initiating devices known in the art, and particularly those referred to above, is that the reliability of these devices is limited due to the application of a single resistive element. Should the element fail, the entire initiating device fails as a result. Although the known initiating devices are used in various fields, there are some fields in which their application is excluded, for the reasons given above.

[0006] Another disadvantage of such initiating devices is that the contact interface between the resistive element and the explosives composition is limited to the size of the surface of the element in contact with the explosives or pyrotechnic composition.

[0007] As electronic integrated circuits of the type used in electronic detonators and other electronically controlled initiators, become relatively smaller through progress of technology, their potential current consumption diminishes accordingly. Hence the energy available to initiate an associated initiation device becomes less. Initiating devices, which operate at elevated energy levels, are therefor undesirable in these applications.

[0008] Electronic control circuits, due to their nature and diminishing capability to handle high levels of energy, require the accompanying resistive initiating device to be of specific resistance and to have a low energy requirement for functioning. They must also have defined energy levels at which they will always function and at which they will definitely not function, the so called all-fire/no-fire energy levels.

[0009] It will be appreciated that the use of a single resistive element will result in an element of which the resistance value and spread in resistance values are dependent on the capability of the process by which the elements are made. Thus thin film bridges will have a highly controllable resistance value with a small spread in values. Wire bridges are similar while the use of conductive compositions results in bridges with a very wide spread in resistance values. Thick film printing provides a spread that is in between the two extremes, for example: thin film +/−10% or less of the nominal value; wires +/−15%; thick film +/−50%; and conductive compositions +/−100 to 1000% of the nominal value.

OBJECT OF THE INVENTION

[0010] It is accordingly an object of the present invention to provide an initiating device for an electronic detonator with which the aforesaid disadvantages may be overcome or at least minimised.

SUMMARY OF THE INVENTION

[0011] According to a first aspect of the invention there is provided an initiating device for an electronic detonator including:

[0012] at least two spaced electrical conductors; and

[0013] a plurality of separate resistive means extending between the electrical conductors, for releasing energy upon application of an electrical current to the resistive means.

[0014] The resistive means may be in the form of bridge elements of a resistive substance.

[0015] The bridge elements may constitute thick film bridges.

[0016] Alternatively the bridge elements may constitute thin film bridges.

[0017] Further alternatively the resistive means may comprise dope substances such as those used in the manufacture of integrated circuits, for creating plasma upon the application of the electrical current.

[0018] Alternatively, the resistive means may be in the form of a wire.

[0019] Further alternatively, the resistive means may constitute a conductive explosive or pyrotechnic composition.

[0020] The resistive means may be imbedded in an explosive or pyrotechnic composition.

[0021] According to a further aspect of the invention there is provided a detonator provided with an initiating device according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention will now be described further by way of non-limiting examples with reference to the accompanying drawings, wherein:

[0023]FIG. 1 is a diagrammatical plan view of an initiating device 10 according to a first embodiment of the invention;

[0024]FIG. 2 is a cross-sectional side view of the initiating device 10 of FIG. 1;

[0025]FIG. 3 is a perspective view of an initiating device 10 b according to a second embodiment of the invention;

[0026]FIG. 4 is a perspective view of an initiating device 10 c according to a third embodiment of the invention;

[0027]FIG. 5 is a plan view of an initiating device 10 d according to a fourth embodiment of the invention; and

[0028]FIG. 6 is a cross-sectional side view along lines B-B¹, in FIG. 5.

[0029] In the drawings, similar or same components are designated with the same numbers.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0030] Referring to FIGS. 1 and 2, according to a first embodiment, the initiating device 10 includes two spaced electrical conductors 12 located on an insulating substrate 14; and two separate resistive means in the form of thick film resistive bridges 16 extending between the electrical conductors 12, for releasing energy upon application of an electrical current to the resistive bridges 16.

[0031] An explosives or pyrotechnic composition, generally designated by reference numeral 18, covers the resistive bridges 16. It will be appreciated that the resistive means need not necessarily be in the form of thick film bridges, but could also be in the form of thin film bridges, wires, dope substances or other resistive substances. There could also be no physical bridge present at all, in which case the resistive path being created by the conductive explosive or pyrotechnic composition itself (see FIGS. 5 and 6).

[0032] The energy requirement of single path resistive initiation devices is linearly dependent on the volume of explosive or pyrotechnic composition heated by the element during the passing of the current. In the case of thick and thin film initiators, the energy requirement is dependent on the physical size of the element. The applicant therefore initially expected that duplication in the number of bridges 16 would lead to a linear concomitant decrease in sensitivity, but has surprisingly found that this is not the case. The use of dual thick film elements resulted in an increase in energy requirement of approximately 25% of the predicted value. This makes the initiating device 10 suitable for use with relatively smaller integrated circuit control devices that operate at relatively lower energy levels, while the reliability of the initiating device 10 is increased with a quadratic amount.

[0033] It will be appreciated that should one of the elements 16 fail, the other element 16 would still initiate the device 10. The size of the contact interface between the resistive elements 16 and the explosives composition 18 is also doubled, making the initiating device 10 even more reliable. As a result the initiating device 10 is suitable for a wide range of different applications.

[0034] The use of two parallel resistive elements, due to the inverse summation of the resistance values to give a resultant single value, leads to lower resistance values than the single element of the known initiators and the spread in values is less. This narrower spread is desirable because it results in more regular operability. This desirable condition can now be obtained from processes hereto unsuitable for the production of highly regular bridges.

[0035] The capability to manipulate the surface area of the resistive element by providing a plurality thereof and without sacrificing the sensitivity of the element in the predicted linear manner, and the use of a plurality of resistive elements further give a designer enhanced flexibility in the manipulation of the all-fire/no-fire levels. This flexibility was previously limited to the capability of the process used to manufacture the elements and to the physical properties of the one element and of the explosive or pyrotechnic composition in which it was imbedded.

[0036] It will be appreciated that variations in detail are possible with an initiating device according to the invention, without departing from the scope of the appended claims. For example, referring to FIG. 3, the initiating device 10 a is provided with three resistive elements 16 b. Further for example, referring to FIG. 4, the electrical conductors 12 c may be embedded by injection molding in an insulating substrate 14 c of plastics material. Referring to FIGS. 5 and 6, the resistive elements may be in the form of bodies 16 d/18 d of a resistive explosives or pyrotechnic composition. Further variations in design are obviously possible without departing from the scope of the claims. 

1. An initiating device for an electronic detonator including at least two spaced electrical conductors; and a plurality of separate resistive means extending between the electrical conductors, for releasing energy upon application of an electrical current to the resistive means.
 2. An initiating device according to claim 1 wherein the resistive means is in the form of bridge elements of a resistive substance.
 3. An initiating device according to claim 2 wherein the bridge elements constitute thick film bridges.
 4. An initiating device according to claim 2 wherein the bridge elements constitute thin film bridges.
 5. An initiating device according to claim 1 wherein the resistive means comprises dope substances such as those used in the manufacture of integrated circuits, for creating plasma upon the application of the electrical current.
 6. An initiating device according to claim 1 wherein the resistive means is in the form of a wire.
 7. An initiating device according to claim 1 wherein the resistive means constitutes a conductive explosive or pyrotechnic composition.
 8. An initiating device according to any one of the preceding claims wherein resistive means is imbedded in an explosive or pyrotechnic composition.
 9. An initiating device substantially as herein described and exemplified.
 10. An electronic detonator provided with an initiating device according to any one of claims 1 to
 9. 